Sound recording system



April 1, 1952 L. B. BROWDER 2,591,045

SOUND RECORDING )SYSTEM Filed Dec. 3d, 1948 lNVEA/TOR L, B; BROWDEH 6V4.n bc A TORNEY Patented Apr. 1, 1952 SOUNDRECORDING. SYSTEM LewisB.'Browder, La Canada; ;G'alif.,- assignor to Western Electric Company,Incorporated, New York, N; Y., a corporation of New YorkApplicationDecember 3Q, 1948', Serial No. 68,230

13 Claims.

-This invention relates to film sound recording systems and particularlyto the recording of original or' direct positive variable area soundrecords with a light valve.

Inknown light valves, light is transmitted between the light valveribbons onto a light-sensitive-film. When the film is developed thenegative or originalsound track develops out into a black variable arearecord, the rest of the track being clear. :When the negative isprinted, the soundtrack develops out into clear film, the rest of thetrack being dark. This print is called the positive.

The object of this invention is to produce an original or directpositive variable area sound recordwitha-light valve.

. Due-.to inhomogenities in the film, a certain amount of ground noiseis produced during the reproduction of the positive sound record. If,however, the positive record is at all times as dark as possible, this.undesired noise will be reduced to a minimum. To produce this result,

[noise reduction bias is applied to the ribbons of conventional lightvalves in a well-known manner as shown, for example, in Patent 1,936,176to R. R. Scoville, issued November 21, 1933. To obtain a positive recordby the use of known light valves two developing operations andajprinting operation are necessary.

. As produced with the presentinvention the original sound track issimilar to the positive obtained with conventional light valves, thusproducing an. original record with a minimum of ground noise.

In accordance with a preferred embodiment of this invention, highlypolished, light-reflecting (o1. ire-100.3)

, 2 monitored by a photoelectric cell or other'suitable means with theadvantage that the amount of light available is considerably greaterthan that obtained from a reflecting prism in the recording opticalpath.

With the application of noise reduction bias to the ribbons, theaperture between the ribbons is'made smaller and the percentage of cleararea in the developed track becomes less and the ground noise in thereproduced film is correspondingly reduced. An original sound recordexposed in this manner has the appearance of a positive, since in thepresent invention the area of the sound track which normally receives noexposure is exposed.

Although current-carrying light-reflecting wires have been previouslyused in oscillographs and'picture transmission devices, these wireconductors are not practicable in a light valve modulator for film soundrecording systems. Mirror oscillographs which may be ,used to produce.

original or positive variable area records are also ribbons are used tointercept a recording light beam projected onto the ribbons and reflectback that portion of the light intercepted by the ribbons onto a movinglight-sensitive film. There is thus formed by the polished ribbonsurfaces image which the ribbons intercept.

a mirrored image of that portion of the filament Since the ribbons movelaterally across the recording beam in response to electrical currents,the position of the 'reflected beam is constantly changing. The

reflected light is of uniform intensity but varies stantaneousdisplacement of the light valve rib- Q;

bons;

The light beam is also transmitted through'ir; the aperture between thelight valve ribbons and iszmodulated by the ribbons in accordance with.

thereon. The transmitted modulated lighti's';

theglvariations in electrical currents impressed producesja variablearea sound track in a new and efficient manner with attendant advantageswhich will be apparent from the description of a preferred embodimentshown diagrammatically on the drawing.

, In the drawing, light from the recording lamp l is directed off thealuminized front surface of the inclined slit mirror 2 into an objectivelens 3. The inclined mirror by which the lightfrom the recording lamp isdirected into the light valve objective lens contains a narrowrectangular. slit extending across its width. The width of this slittogether with the reduction afforded by the objective cylinder lensdetermines the height of the recording image. The recording lamp isofthe prefocussed type having a single helix, straight, horizontalfilament. The axis of the filament is rotated at 45 degrees to theoptical axis which has the effect of reducing the pitch of the filamenthelix to 'the point where there rents flowing lengthwise through theribbons will,

cause them to move laterally in a common plane. The light valve of thepresent invention differs from that disclosed in the Wente patent byhaving the holes in the magnet pole-pieces pierced large enough topermit the light valve ribbons to be completely illuminated during theircomplete excursions when fully modulated by sound currents.

The ribbons may be connected to record either a. bilateral or aunilateral type of variable area sound track. For a bilateral soundtrack, the ribbons may be connected by wires 1 and to the recordingcircuit of a sound recording system as shown, for example, in the R, R.Scoville patent mentioned above. If desired, one of the ribbons may beconnected to move in response to noise reduction currents while theother moves in response to speech currents. Obviously, in

cases where it is desirable, electrical currents may be applied to onlyone of the ribbons while the other ribbon or any suitable reflector maybe used as a stationary reflectorto cooperate with the vibrating ribbonto produce a positive unilateral variable area sound track.

The ribbons may be made of polished and aluminized Phosphor bronze,beryllium copper, or any other suitable highly reflecting material.Extremely good results were obtained by using aluminum foil. It has beenfound that optical polishing of the rolled foil leaves occasionalscratches which, since the ribbon surface is imaged on the film, appearas clear streaks in the sound track. Highly satisfactory results havebeen obtained by careful maintenance of the rolls with which the foil isworked. Excellent foil surfaces have thus been obtained having a veryhigh reflectance. The width of the ribbons is considerably larger thanthe thickness. The thin, flat ribbons appear as a thin strip mirrorwhose surface is perpendicular to both the optical axis and the axis ofthe recording beam.

Thewidth of each ribbon strip is defined by the accurately space'd edgesof the ribbon and is considerably less in extent than half of the widthof the recording beam. The recording beam is sufliciently wide tocompletely cover the outer edges of the ribbons in their outermostpositions when fully modulated by sound currents. There is thus formedby the polished ribbon surfaces a mirrored image of that portion of therecording beam which the ribbons intercept.

Since the ribbons move laterally across the recording beam in responseto modulation currents, they reflect moving beams of light back towardthe light valve objective lens 3. The light valve objective lens thenpicks up the reflected images and projects them through the slit in theinclined mirror. The light passes through the slit to a front surfacealuminized mirror 9 whose function is to turn the recording beam through90 degrees to a horizontal axis. A cylindrical lens ll located near thefilm gathers the beam of light from the slit and converges it to thenarrow line required for the recording image and focusses it onto thefilm 8. The film 8 is moved at constant speed by the usual film drive(not shown).

A slit mask 16 is located at the cylindrical lens II to limit the extentof the exposed portion of the direct positive sound track so that theexcursions of the outer edges of the ribbons are not recorded on thetrack. If the outer edges were recorded onthe film the varying outside.edges would introduce additional signal currents during reproduction andthus impair the fidelity of the reproduction A sound. track produced inaccordance with this invention is suitable for reproduction in astandard film sound reproducing machine.

The modulated light also passes through the aperture between the ribbonsupward through a slit in a mask [2. This mask is provided to prevent anystray light which may pass around the outer edges of the ribbons fromreaching the condenser lens I3. The lens 13 focusses the modulated lightonto a prism in alight conducting rod I4. The function of the prism isto turn the recording beam through degrees to a horizontal axis anddirect the modulated light onto a suitable monitoring photoelectric celll5. However, it is obvious that it is not necessary that the modulatedbeam be turned 90 degrees, for the modulated beam may be projecteddirectly onto the photoelectric cell.

Recording of a negative variable area record is accomplished with thesame light valve by interchanging the recording lamp and thephotoelectric cell. With the recording lamp in position along theoptical center line of the light valve, the beam is deflected downwardby the prism in the light conducting rod to the condenser lens l3. Animage of the lamp filament is focussed by the condenser lens slightlybeyond the ribbon plane in order to further minimize the effect of thefilament striations. The rear-illuminated aperture between the ribbonsis then projected by the light valve objective lens through the slit andto the film. As in the direct positive set-up, the cylinder lensfocusses the slit onto the film emulsion to define the height of therecording image.

Light for photocell monitoring in the recording of negative variablearea sound records is obtained from the excess of the light over thatpassing through the slit of the inclined mirror and is directed to thephotocell which has been placed in line with the reflecting surface ofthe mirror along a horizontal axis.

Thus, by interchanging the positions of the exciting lamp and monitoringphotoelectric cell, either standard negative or direct positiverecording may be accomplished.

What is claimed is: 1. In a sound recording system, a movinglightsensitive film, a source of light, a pair of spaced lightreflecting current-carrying ribbons disposed in the light beam from saidlight source, means disposed between said light source and said ribbonsfor imaging the reflecting surface of said ribbons at said film andmeans for vibrating said ribbons to produce a record on said film.

2. In a sound recording system a moving lightsensitive film, a source oflight, a pair of spaced light reflecting current-carrying ribbonconductors, means for directing said light onto said ribbons, means forvibrating said ribbons'transversely of said film, said ribbons in turnreflecting said light onto said film to produce a direct positivevariable area record thereon.

3. In a film sound recording system, a moving light-sensitive film, asource of light, a pair of spaced current-carrying reflecting ribbons, amirror having an aperture therein, said mirror being arranged to directsaid light onto said ribbons, said ribbons in turn reflecting said lightthrough the aperture of the mirror onto the lightspaced current-carryingreflecting ribbons, a mirror having an aperture therein, said mirrorbeing arranged to reflect said light, means for focussing said lightonto said ribbons, said ribbons in turn reflecting said light andredirecting it to said focussing means to project said light through theaperture of the mirror onto the light-sensitive film to produce a directpositive variable area record on said film in accordance with electricalcurrents impressed upon said ribbons.

5. In a film sound recording system, a source of sound modulatedcurrents, means producing a beam of light, a pair of spaced lightreflecting ribbons disposed in said light beam, a moving light sensitivefilm disposed in the path of light reflected from said ribbons, saidribbons being electrically connected to said source of currents andmovable transversely of said film in response to variations in saidcurrents to produce a direct 1 positive variable area sound record onsaid film.

6. In a film sound recording system, means producing a beam of light, alight reflecting ribbon, a source of sound modulated currentselectrically connected to said ribbon to produce movement thereof inresponse to variations in said currents, a moving light sensitive film,a centrally apertured light deflecting means positioned in said lightbeam to deflect said beam toward said reflecting ribbon, and a singleoptical means positioned between said deflecting means and said ribbonfor imaging said light beam at said ribbon and for imaging said ribbonat the plane of said film through the aperture in said light deflectingmeans.

7. In a system for photographically recording a direct positiveunilateral variable area sound track, a source of sound modulatedcurrents, means producing a beam of light, a pair of spaced lightreflecting ribbons disposed in said light beam, a moving light sensitivefilm disposed in the path of light reflected from said ribbons, saidsource of currents being electrically connected to one of said pair ofribbons to produce movement thereof toward and away from the other ofsaid pair of ribbons in response to variations in said current source.

8. In a sound recording system, a moving lightsensitive film, a sourceof light, a pair of spaced light reflecting current-carrying ribbonsdisposed in the light beam from said light source, means disposedbetween said light source and said ribbons for imaging the reflectingsurface of said ribbons at said v film, means for vibrating said ribbonsto produce a record on said film, and means disposed on the oppositeside of said ribbons from said imaging means for monitoring that portionof the light beam which passes through the space between the ribbons.

9. In a sound recording system a moving lightsensitive film, a source oflight, a pair of spaced light reflecting current-carrying ribbonconductors, means for directing said light onto said ribbons, means forvibrating said ribbons transversely of said film, said ribbons in turnreflecting said light onto said film to produce a direct positivevariable area record thereon, and means disposed on the opposite side ofsaid ribbons from said film for monitoring that portion of the lightbeam which passes through the space between the ribbons.

10. In a film recording system, a moving lightsensitive film, a sourceof light, a pair of spaced current-carrying reflecting ribbons, a mirrorhaving an aperture therein, said mirror being arranged to direct saidlight onto said ribbons, said ribbons in turn reflecting said lightthrough the aperture of the mirror onto the light-sensitive film toproduce a direct positive variable area record on said film inaccordance with electrical currents impressed upon said ribbons, andmeans for monitoring that portion of the light beam which passes throughthe space between the ribbons.

11. In a film recording system, a moving lightsensitive film, a sourceof light, a pair of spaced current-carrying reflecting ribbons, a mirrorhaving an aperture therein, said mirror being arranged to reflect light,means for focussing said light onto said ribbons, said ribbons in turnrefiecting said light and redirecting it to said focussing means toproject said light through the aperture of the mirror onto thelight-sensitive film to produce a direct positive variable area recordon said film in accordance with electrical currents impressed upon saidribbons, and means for monitoring that portion of the light beam whichpasses through the space between said ribbons.

12. In a film sound recording system, a source of sound modulatedcurrents, means producing a beam of light, a pair of spaced lightreflecting ribbons, disposed in said light beam, a moving lightsensitivefilm disposed in the path of light refiected from said ribbons, saidribbons being electrically connected to said source of currents andmovable transversely of said film in response to variations in saidcurrents to produce a direct positive variable area sound record on saidfilm, and means disposed beyond said spaced ribbons in the path of thelight beam which passes therebetween for monitoring the sound beingrecorded on said film.

13. In a system for photographically recording a direct positiveunilateral variable area sound track, a source of sound modulatedcurrents, means producing a beam of light, a pair of spaced lightreflecting ribbons disposed in said light beam, a moving light-sensitivefilm disposed in the path of light reflected from said ribbons, saidsource of currents being electrically connected to one of said pair ofribbons to produce movement thereof toward and away from the other ofsaid pair of ribbons in response to variations in said current source,and a photoelectric cell disposed in the path of said light beam passingbetween said ribbons whereby the sound being recorded on said film maybe monitored during recording.

LEWIS B. BROWDER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS \Number Name Date 1,638,555 Wente Aug. 9, 19271,847,636 Taylor Mar. 1, 1932 2,101,940 Hansen Dec. 14, 1937 2,108,815Gille Feb. 25, 1938 2,147,623 Wender Feb. 14, 1939 2,289,054 DimmickJuly 7, 1942 FOREIGN PATENTS Number Country Date 370,422 Great BritainApr. 6, 1932 498,394 Great Britain Jan. 6, 1932

